HR: 16:15h
AN: NS24A-02 INVITED    [Abstracts]
TI: Basin Structure Beneath the Santa Rosa Plain, Northern California: Implications for Damage Caused by the 1969 Santa Rosa and 1906 San Francisco Earthquakes
AU: * McPhee, D K
EM: dmcphee@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Langenheim, V E
EM: zulanger@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Hartzell, S
EM: shartzell@usgs.gov
AF: U.S. Geological Survey, MS 966 PO Box 25046, Denver, CO 80225, United States
AU: McLaughlin, R J
EM: rjmcl@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Aagaard, B T
EM: baagaard@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Jachens, R C
EM: jachens@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: McCabe, C A
EM: cam509@psu.edu
AF: Department of Geography, Pennsylvania State University, 337 Walker Building, University Park, PA 16802, United States
AB: Regional gravity data in the northern San Francisco Bay region reflect a complex basin configuration beneath the Santa Rosa plain that likely contributed to the significant damage to the city of Santa Rosa caused by the 1969 M 5.6, 5.7 Santa Rosa earthquakes and the 1906 M 7.9 San Francisco earthquake. Inversion of these data indicates that the Santa Rosa plain is underlain by two sedimentary basins about 2 km deep separated by the Trenton Ridge, a shallow west-northwest-striking bedrock ridge west of Santa Rosa. The city of Santa Rosa is situated above the 2 km-wide protruding northeast corner of the southern basin where damage from both the 1969 and 1906 earthquakes was concentrated. Using the gravity-defined basin geometry, ground motion simulations of the 1969 and 1906 earthquakes, two events with opposing azimuths, show enhanced ground motions along the northeastern edge of this corner suggesting that basin-edge effects contributed to the concentration of shaking damage in these events. This indicates that basin edge effects will likely contribute to strong shaking in this area during future earthquakes. Characterization of low-velocity basins and their detailed three-dimensional subsurface geometry is an essential component for characterizing the seismic hazard in the northern San Francisco Bay region and elsewhere.
DE: 0920 Gravity methods (1219)
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 7212 Earthquake ground motions and engineering seismology
DE: 8015 Local crustal structure
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting